Method and apparatus for measuring intra-ocular pressure



April 19, 1966 W. L. HYDE METHOD AND APPARATUS FOR MEASURINGINTRA-OCULAR PRESSURE 2 Sheets-Sheet 1 Original Filed Nov. 17, 1960 HTTOBNEYS m EH mm NW Wu N m w w W. L. HYDE A ril 19, 1966 METHOD ANDAPPARATUS FOR MEASURING INTRA-OCULAR PRESSURE Original Filed Nov. 17.1960 2 Sheets-Sheet z Z i l M m m E A 4i I II .L X A A k m a o m 2 t. m

I N VE N T02 WHLTEE LEW/5 HYDE 7/ ifi wa Q (My;

QTTOENEYS United States Patent 3,246,507 METHOD AND APPARATUS FORMEASURING INTRA-OCULAR PRESSURE Walter Lewis Hyde, Pittsburgh, Pa.,assignor to American Optical Company, Southbridge, Mass, a voluntaryassociation of Massachusetts Continuation of application Ser. No.69,948, Nov. 17, 1960. This application Apr. 5, 1963, Ser. No. 271,01620 Claims. (Cl. 73-80) This application is a continuation of mycopending application Serial No. 69,948, field November 17, 1960, andnow abandoned.

The field of this invention is that of tonometry, and the inventionrelates, more particularly, to a novel and improved tonometer and to anovel and improved method to tonometry.

As is well known, the pathological eye disorder known as glaucoma ischaracterized by increasing intraocular pressure which can ultimatelylead to destruction of the eye. When this disorder has developed intoits more advanced stages, progressive deterioration of the eye isdiflicult or impossible to halt and usually results in total blindnessin the eye so that detection if incipient glaucoma at the earliestpossible moment is of the highest importance. -At the present time, itis conventional practice to measure intraocular pressure or the tone ofan eye as it is called for detecting incipient glaucoma as well as forother reasons, and various ton ometers and methods of tonometry havebeen developed for this purpose. Known conventional tonometers utilize arigid plunger member or members which directly engage and exert apressure against the cornea of an eye with measured force for depressingthe cornea against intraocular pressure and which measure the extent towhich the cornea is depressed or indented as an indication ofintraocular pressure. As will be readily understood, the pressing of ahard plunger against the cornea exposes the cornea to risk of injury,particularly :where substantial depression of the cornea may berequired. I I

It is an object of this invention to provide a novel and improved methodof tonometry; to provide a method of tonometry by which intraocularpressure can be accurately measured without risk of injury to the corneaof the eye; to provide such a method of tonometry which does not requirecontact between the eye and any hard or unyielding objec-t; to providesuch a method of tonometry by which intraocular pressure can beaccurately determined with minimum depression of the cornea; and toprovide such a method of tonometry which can be rapidly andconventiently performed. It is a further object of this invention toprovide a novel and improved tonometer; to provide a tonometer which canbe utilized for measuring intraocular pressure without risk of injury tothe cornea of an eye; to provide such a tonometer which does not requirecontact between an eye and any hard, unyielding object; to provide sucha tonometer which can measure intraocular pressure with speed,convenience and accuracy; and to provide such a tonometer which issimply and inexpensively constructed.

Briefly described, the novel and improved method of tonometry providedby this invention includes the steps of establishing a plurality offluid passages having respective open ends, projecting streams of fluidfrom respective passages through the open ends thereof with diiferentforces so that at least one stream of fluid is projected with suflicientforce to indent an eye, establishing a spatial relationship'between theopen passage ends and an eye so that the open passage ends aresubstantially restricted by the eye and so that the eye is indented byat least said one stream of fluid, and measuring or sensing fluidpressures within said passages as an indication of intraocular pressure.

A preferred method of tonometry provided by this invention includes thesteps of establishing a plurality of fluid passage having respectiveopen ends, and projecting streams of fluid from respective passages sothat a stream of fluid is projected from at least one passage withsufficient force to indent an eye and so that a stream of fluid isprojected from at least one other passage with less force than isrequired to indent an eye. For example, a pair of fluid passages can beestablished having respective open ends in side-.by-side, concentric orother predetermined relation and a stream of fluid can be projected fromone passage with an applied pressure greater than 60 millimeters ofmercury so that the stream of fluid is adapted to indent an eye againstthe force of intraocular pressure even where intraocular pressure may beincreased by a pathological disorder such a glaucoma. Where the openpassage ends are disposed in concentric relation, this stream of fluidis preferably projected from the inner passage. A stream of fluid can beprojected from the other passage with an applied pressure less than 10millimeters of mercury so that the stream of fluid is adapted to bedirected upon an eye without indenting the eye against the force ofnormal intraocular pressure. In this arrangement, the open passage endscan be positioned relative to an eye so that the eye substantiallyrestricts the open passage ends, whereby fluid pressures within thepassages will increase to approach the applied pressures by which saidstreams of fluid are projected. Where the passage ends are locatedrelatively close to the eye, fluid pressure increases within thepassages will be very closely related to the extent to which the openpassage ends are restricted by the eye. Since the stream of fluidprojected from said other passage is not adapted to indent or depressthe eye, the fluid pressure in that passage indicates the extent towhich the open end of the passage is restricted by the eye and willtherefore be an extremely accurate measure of the spacing of the passageends from the eye. On the other hand, since the stream of fluidprojected from said one passage is adapted to indent or depress the eye,fluid pressure in that one passage will indicate greater spacing of thepassage ends from a depressed portion of the eye and will therefore be ameasure of the extent to which the eye is indented or depressed by thestream of fluid projected from that passage. As will be understood, theextent to which the eye is indented by a stream of fluid exerting aknown force can comprise an indication of intraocular pressure. Mostadvantageously, the position of the passage ends relative to an eye canbe adjusted until fluid pressure within said other passage is increasedto a predetermined level for indicating that the passage ends arelocated in a predetermined, preferred position relative to the eye. Thenfluid pressure in said one passage can be measured as an indication ofintraocular pressure. Preferably, also, the fluid pressure within saidone passage is measured automatically when fluid pressure in said otherpassage is increased to said predetermined level, whereby the passageends need be maintained in the preferred position relative to the eyefor a minimum period of time.

Alternatively, three fluid passages can be established having respectiveopen ends disposed in side-by-side, linear relation. If desired, streamsof fluid can be projected. from respective passages so that the streamof fluid projected from the center passage has suflicient force toindent an eye and so that streams of fluid projected from the outerpassages have less force than is required for indenting an eye.Conversely, if desired, a stream of fluid can be projected from thecenter passage with less force than is required for indenting an eye andthe streams of fluid projected from the outer passages can be projectedwith said greater force. In this arrangement, the fluid pressure in thepassage or passages from which fluid is projected with a relativelysmall applied pressure can indicate the position of the passage endsrelative to the eye in the manner above described. The fluid pressuresin the outer passages can be brought into balance whether the streams offluid projected from said outer passages are projected with relativelylow or relatively high pressure, thereby to assure that the passages arealigned with a radius of the cornea of the eye. Fluid pressures in thepassage or passages from which streams of fluid are projected withrelatively high pressures can then be measured or sensed as anindication of intraocular pressure as described above.

In a preferred method of tonometry according to this invention, there isprovided a pliable protecting film which is placed in coextensivesuperposition upon the cornea of the eye prior to measurement ofintraocular pressure in the manner above described, thereby to shieldthe eye from abrasive materials which might be carried in said streamsof fluid and to prevent drying of the surface of the eye where saidstreams of fluid comprise streams of air and the like.

The novel and improved tonometer provided by this invention includesmeans having a plurality of passages therethrough, the passages havingrespective open ends which are preferably arranged in predetermined,closelyspaced relation to each other. For example, a pair of tube meanshaving respective open ends can be mounted or secured together forholding the open tube ends in side-by-side, concentric or otherpredetermined relation. The tonometer also includes means projectingstreams of fluid from respective passages through the open ends thereofso that at least one stream of fluid is projected with sufficient forceto indent an eye and preferably so that at least one stream of fluid isprojected with less force than is required for indenting an eye. Wherethe tonometer incorporates a pair of tube means having respective openends in concentric relation, said means are preferably provided forprojecting a stream of fluid from the inner passage end with suflicientforce to indent an eye. The tonometer also includes pressure-responsivemeans for sensing or measuring fluid pressures within said passages asan indication of intraocular pressure.

In a practical embodiment of this invention, the tonometer includesthree tube means having respective open ends, the tube means beingmounted for holding the open tube ends in side-by-side linear relationto each other. Means are provided for projecting a stream of fluid fromthe center passage with suflicient force to indent an eye and means areprovided for projecting streams of fluid from the outer passages withless force than is required for indenting an eye. Conversely, ifdesired, means are provided for projecting streams of fluid from theouter passages with suflicient force to indent an eye and means areprovided for projecting a stream of fluid from the center passage withless force than is required for indenting an eye. This embodiment of thetonometer also incorporates pressure-responsive means for measuring orsensing fluid pressures within said passages as an indication ofintraocular pressure.

In a preferred embodiment of this invention, the tonometer includes apair of tube means having respective open ends, the tube means beingmounted for holding said open tube ends in predetermined, closelyspacedrelation. Means are provided for projecting a stream of fluid from onepassage with sufficient force to indent an eye, and means are providedfor projecting a stream of fluid from the other passage with less forcethan is required for indenting an eye. First manometer meansincorporated in the tonometer includes a column of liquid movable in amanometer tube, the manometer tube being associated with said one tubemeans so that the liquid level in the tube is adapted to indicate fluidpressure within the one tube means. Electrically actuable valve meansare disposed within the manometer tube and are adapted to fix the liquidlevel in the tube when actuated, thereby to maintain the liquid level inthe tube as a record of fluid pressure within said one tube means at thetime the valve means is actuated. Second manometer means are associatedwith the other tube means for measuring or sensing a predetermined fluidpressure within the other tube means, the second manometer meansincluding means for closing an electrical circuit to actuate said valvemeans automatically when fluid pressure is sensed or measured by saidsecond manometer means as having reached said predetermined level.

Preferably, the first manometer means includes means for detachablymounting a scale adjacent said manometer tube, and the tonometerincludes a plurality of scales adapted to be selectively mountedadjacent said manometer tube. The scales each have divisions spaced toindicate intraocular pressures corresponding to liquid levels in themanometer tube for respective corneal curvatures. That is, thegraduations of the scales are calibrated relative to respective eyeshaving particular corneal curvatures. The tonometer can then bepositioned relative to an eye having a corneal curvature correspondingto that for which a particular scale has been calibrated forsubstantially restricting the open tube ends, thereby to increase fluidpressures within said tube means until said valve means are actuated forfixing the liquid level in said manometer tube. The liquid level in saidmanometer tube then indicates fluid pressure in said one tube means. Byheading the graduation of a scale calibrated for said corneal curvaturewhich has been selectively mounted adjacent the manometer tube, thisfluid pressure measure can be interpreted as a corresponding measure ofintraocular pressure for the eye.

Other objects, advantages and details of the tonometers and method oftonometry provided by this invention will appear in the followingdescription of preferred embodiments of the invention, the descriptionreferring to the drawing in which:

FIG. 1 is a partial side elevation view partially in section of thetonometer provided by this invention illustrating association of thetonometer with an eye for intraocular pressure;

FIG. 2 is a View similar to FIG. 1 illustrating the function of thedevice of FIG. 1;

FIG. 3 is a view similar to FIG. 1 illustrating an alternativeembodiment of the device of FIG. 1;

FIG. 4 is a view similar to FIG. 1 illustrating another alternativeembodiment of the device of FIG. 1;

FIG. 5 is a view similar to FIG. 1 illustrating another alternativeembodiment of the device of FIG. 1; and

FIG. 6 is a graph representing the relationship between spacing of thetonometer from an eye and fluid pressures in the tonometer passages.

Referring to the drawings, FIGS. 1-5 illustrate part of an eye 10showing the relationship between the cornea 12 and the anterior chamber14 of an eye. As can be seen, the cornea is disposed so that the fluidpressure of the aqueous humour which resides in the anterior chamber isexerted. directly upon the cornea and holds the elastic corneal tissuein a distended condition as shown. In a norm-a1 eye, the fluid pressurewithin the eye, or the intraocular pressure as it is called, can rangefrom 11.5 to 30 millimeters of mercury with most eyes having anintraocular pressure between 20 and 25 millimeters of mercury. However,in a diseased eye suffering the disorder known as glaucoma, intraocularpressure can increase to as much as 60 millimeters of mercury in acutestages of the disorder.

A preferred embodiment of the tonometer provided by this invention isindicated at 16 in FIGS. 1-3, the tonometer including a tube 18 havingan open end 18.1 The tube 18 is connected as at 18.2 to a source ofcompressed air 19 so that a stream of compressed air is projectedthrough the tube passage 18.3 from the open tube end 18.1. The source ofcompressed air can be of any conventional type but is preferably adaptedto project a stream of air through the tube 18 with a maximum appliedpressure of less than millimeters of mercury. In such an arrangement,the fluid pressure within the open-ended passage 18.3 will normally besubstantially less than 10 millimeters of mercury but, as will beunderstood, if the open end 18.1 of the tube is closed, fluid pressurewithin the tube passage will rise to equal the applied pressure.

The tonometer16 also includes another tube 20 which has an open end20.1, this tube being connected as at 28.2 to another source ofcompressed air 22. The tube 20 is mounted within the tube passage 18.3so that the open tube ends 18.1 and 20.1 are arranged in fixed,concentric relation. For example, as illustrated, the tube 20 can bebrazed, soldered or otherwise secured to the tube 18 as at 24 forholding the open tube ends in said predetermined, closely-spacedrelation. The compressed air source 22 can also be of any conventionaltype but is preferably adapted to project a stream of air through thetube passage 20.3 with a minimum applied pressure greater than 60millimeters of mercury. In this arrangement, fluid pressure within thetube passage 20.3 will normally be substantially less than 60millimeters of mercury, but if the open tube end 20.1 is closed, fluidpressure within the tube passage will rise to equal the appliedpressure. It should be understood that although streams of air aredescribed herein, streams of any other suitable fluid such as distilledwater or the like could be projected from the tubes 18 and 20 within thescope of this invention. The tubes 18 and 20 can be formed of metal,plastic or any other suitably strong and rigid material which has areasonable degree of dimensional stability under various pressures.

Each of the tubes 18 and 20 is connected to a manometer tube, 24 and 26respectively, each manometer tube having a goosenecked portion, 24.1 and26.1 respectively, which is filled with a relatively heavy liquid 28 and29 respectively in conventional manner. As will be readily understood,the manometer tubes are connected to the tubes 18 and 20 so that thecolumns of liquid 28 and 29 in the left-hand portions of the manometertubes are exposed to fluid pressures within the passages 18.3 and 20.3.Thus, the columns of liquid, preferably columns of mercury, are adaptedto rise and fall in the right-hand portions of the goosenecks 24.1 and26.1 as fluid pressures in the passages 18.3 and 20.3 increase anddecrease so that the levels 28.1 and 29.1 of the liquids 28 and 29 inthe tubes 24 and 26 comprise a measure of the fluid pressures in thepassages 18.3 and 20.3 respectively.

As shown in FIGS. 1-3, the tubes 18 and 20 can be moved together and canbe positioned relative to the eye 10 so that the cornea 12 of the eyesubstantially restricts the open ends 18.1 and 20.1 of the tubes. Asindicated by the arrows 30 in FIG. 2, restriction of the tube endsretards the flow of streams'of fluid from the tube ends so that fluidpressures within the tube passages 18.3 and 20.3 will increase toapproach the applied pressures by which the streams of fluid areprojected. As shown in the graph of FIG. 6, the fluid pressures withinthe passages 18.3 and 20.3 are related to the spacing T and T (see FIGS.1 and 2) between the open tu be ends 18.1 and 20.1 and the cornea 12 sothat as the open tube ends are brought close to the eye, fluid pressureP in the passage 18.3, for example, will increase at a slow rate. Then,as the space T between the tube end and the eye is further reduced,fluid pressure P in the passage 18.3 will increase more rapidly. Whenthe space T between the tube and eye becomes very small, very slightreduction in the spacing T will cause a substantial increase in fluidpressure P. Thus where the space T is small, the fluid pressure P in thepassage 18.3 becomes a very accurate measure of the space T.

It has been noted that the stream of fluid projected from the tube 18 isprojected with a maximum applied pressure less than 10 millimeters ofmercury which is also less than normal intraocular pressure. Thus, thestream of fluid projected from the tube 18 is projected with less forcethan is required for indenting or depressing the cornea 12 against theforce of intraocular pressure. Accordingly, as the tube ends 18.1 and20.1 are restricted by the cornea 12 so that fluid :pressures in thepassages 18.3 and 20.3 increase, the stream of fluid projected from thetube 18 will not depress the eye and the fluid pressure in the tube 18will comprise a measure of the space T between the tube end 18.1 and anunderpressed portion of the cornea 12. Thus, fluid pressure in thepassage 18.3 can be said to be a gauge for locating the tube ends 18.1and 20.1 relative to the cornea. For example, the tubes 18 and 20 can beadjusted relative to the eye 12 until fluid pressure in the tube 18, assensed or measured by the manometer tube means 24, reaches apredetermined level, thereby to locate the tube ends 18.1 and 20.1 in apredetermined position relative to the eye. It has also been noted thatthe stream of fluid projected from the tube 20 is projected with aminimum applied force greater than 60 millimeters of mercury which isalso greater than intraocular pressure, this applied force being greaterthan intraocular pressure likely to be encountered even in an eyesuffering acute glaucoma. Thus, as the tube ends 18.1 and 20.1 arepositioned relative to the eye for restricting the tube ends so thatfluid pressures in the tubes increase, the fluid pressure in thispassage 20.3 will approach said applied pressure and the stream of fluidprojected from the tube end 20.1 will have sufficient force to indent ordepress the eye. In the manner described above with reference to thespacing T, the fluid pressure in the tube 20 comprises an indication ofthe spacing T between the open passage end 20.1 and the cornea 12.However, since the stream of fluid projected from the tube end 20.1 isadapted to depress the cornea, the space T will represent the distancebetween the tube end 20.1 and a portion 12.1 (see FIGS. 2 and 3) of thecornea which has been depressed by the stream of fluid.

As will be understood, when the space T has been established between thetube end 18.1 and an undepressed portion of the cornea 12, the locationof the tube end 20.1 relative to undepressed portions of the eye hasalso been established. Then the space T between the tube end 20.1 andthe depressed portion 121 of the cornea is an indication of the extentto which the cornea has been depressed by the stream of fluid projectedfrom the tube end 20.1. The extent to which the cornea is depressed by aknown fluid pressure exerted through the passage 20.3 is then, in turn,an indication of the intraocular pressure which tends to hold the corneafully distended.

The manometer tube 24 can be composed of any suitable material butpreferably the gooseneck portion 24.1 of the tube, or the right-handportion of the tube as illustrated, is formed of an electricallyinsulating material such as glass or the like. The tube 24 has apertures24.2 and 24.3 which are arranged in spaced relation to receive terminals32 and 34, the terminals preferably being secured within the apertureswith an adhesive or other suitable means for sealing the apertures. Theterminals are then adapted to be electrically interconnected by theliquid 28 within the tube if the liquid comprises an electricalconductor such as mercury. As will be understood, the terminal can bespaced so that they are adapted to be electrically interconnected by theliquid 28 only when fluid pressure in the passage 18.3 has increased toa predetermined level suflicient to cause the level 28.1 of the liquid28 to contact the upper terminal 32. Of course, if the tube 24 is notcomposed of an electrically insulating material, the terminals 32 and 34can be insulated from the tube in any conventional manner so that theterminals will be electrically interconnected only when the liquid 28has risen to the desired level.

The manometer tube 26 can also be composed of any suitable material, butpreferably the gooseneck portion 26.1 of the tube is formed oftransparent material such as glass whereby the level 29.1 of the liquid29 within the tube can be viewed. An electrically actuable valve 36,such as a conventional solenoid valve, can be disposed within themanometer tube 26 and can be adapted for preventing movement of thecolumn of liquid 29 Within the tube. That is, the valve 36 can benormally open to permit the level of the liquid 29 to rise and fall inresponse to fluid pressure in the passage 20.3. However, the valve isadapted to close when actuated for preventing further movement of theliquid in the tube 26, thereby to fix or maintain the level of theliquid to indicate and record the fluid pressure within the passage 20.3at the instant the valve was actuated. Preferably, the valve is of thetype which must be manually returned to open position or whichincorporates a time delay means of any conventional type for holding thevalve closed for a reasonably long period after actuation before it willautomatically open. The valve 36 is interposed in series relation to apower source such as the battery 38 through the terminals 32 and 34 sothat the valve is adapted to be actuated when the terminals areelectrically interconnected by the liquid 28.

In this arrangement, the tubes 18 and 20 can be adjusted relative to thecornea 12 of an eye until the open tube ends 18.1 and 20.1 aresubstantially restricted so that fluid pressure in the passage 18.3 hasincreased to a predetermined level, thereby to locate the tube endsrelative to the undepressed surface of the cornea. As will beunderstood, this level can be selected to be reached when the space Tbetween the tube end 18.1 and the cornea is very small so that thedesired location of the tube ends relative to the eye can be accuratelyachieved. Further, this level can be selected to be reached when thepressure in passage 20.3 has increased so that the stream of fluidprojected from the passage 20.3 is adapted to indent or depress thecornea. The terminal 32 is positioned within the manometer tube 24 sothat the level 28.1 of the liquid in that tube will be raised to contactthe terminal 32 when fluid pressure in the passage 18.3 has reached saidpredetermined level. At the in stant the liquid 28 contacts the terminal32, the valve 36 will be automatically actuated to closed position sothat further movement of the liquid in the manometer tube 26 in responseto changing pressures in the passage 20.3 is prevented. Thus, the liquidlevel 29.1 in the tube 26 will be maintained at the level it had reachedat the instant the valve was actuated and will therefore indicate thefluid pressure in the passage 20.3 at the instant the predeterminedfluid pressure in the passage 18.3 had been reached. The liquid level29.1 can then be interpreted to indicate intraocular pressure within theeye 10. Since the valve 36 will not immediately return to open position,there will be ample time for the operator of the tonometer to make anaccurate reading of the liquid level 29.1.

As will be understood, the streams of fluid projected from the tube ends18.1 and 29.1 in the tonometer 16 must both pass between the cornea 12and the tube 18.1 through the space T so that fluid pressures in thetube passages are likely to be effected by such factors as the relativediameters of the tubes and by the relationship of the pressures in thepassages. Further, mechanical variations in construction of the device16 as well as many other factors will also play a part in determiningthe fluid pressures which will exist in the tube passages. Accordingly,it may be desirable to calibrate each tonometer 16 individually so thatthe liquid level 29.1 in the manometer tube 26 can be read against ascale, such as the scale 40, mounted adjacent the tube 26 for providinga direct reading of the intraocular pressure measured by the tonometer.As will be understood, calibration of the scale 4!) can be achieved inconventional manner by testing the tonometer 16 against known standards.For example, the device 16 can be tested upon eyes of known intraocularpressure.

It will also be noted that the radius of curvature of the cornea 12plays a part in determining the relationship between the spaces T and Tthe spaces between respective tube ends and the cornea 12. For thisreason, the diameters of the tubes 18 and 20 are preferably small, forexample having inside diameters of two millimeters and one millimeterrespectively, for limiting the significance of the corneal curvature.Alternatively, 'a plurality of scales similar to scale 40, etc. can beprovided which are individually calibrated for eyes of different cornealcurvature. Then, after measurement of the corneal curvature of aparticular eye, the appropriate scale can be selectively mountedadjacent the manometer tube 26 by means of the detachable brackets 41,so that the liquid level in the tube 26 can be read directly to indicateintraocular pressure of that particular eye.

It should be understood that although the manometer tube 24 is providedwith terminals 32 and 34 for actuating the valve 36, any other suitablepressure-responsive means could be associated with the tube 18 foractuating the valve 36 or other similar means in response to fluidpressure in the passage 18.3. Further, although the tubes areillustrated to show that the tube ends are located in the same plane,the tube ends 18.1 and 20.1 could be located in spaced, parallel planesif desired. It should also be noted that it may be desirable toanesthetize the eye prior to testing with the tonometer device 16 toassure a degree of immobility in the eye and to prevent discomfort tothe patient.

The tonometer 42 which is partially illustrated in FIG. 4 comprises analternative embodiment of this invention. As illustrated, the device 42'incorporates a pair of tubes 44 and 46 which are similar to the tubes 18and 20 respectively, these tubes being secured in side-by-side relationby a bracket 48. Except for the fact that the tube ends are located inside-by-side relation, the device 4-2 is identical to the tonometer 16previously described. If desired, a protective place 49 such as apliable plastic film can be disposed in coextensive superposition withthe cornea of the eye for shielding the eye from abrasion due toparticles which might be carried in said streams of fluid and forpreventing drying of the cornea where streams of air and the like areutilized.

The tonometer 5t) partially shown in FIG. 5 comprises anotheralternative embodiment of this invention. In this device, three tubes52, 54 and 56 having respective open ends 52.1, 54.1 and 56.1 aresecured together by a bracket 53 for holding the open tube ends inside-by-side linear relation. The tubes are connected to sources ofcompressed air (not shown) in a manner similar to that described withreference to the device 16 so that streams of air are projected from theopen tube ends. The stream of air projected from the center tube 54 canbe projected with an applied force so that the stream has less forcethan is required to indent or depress the cornea of an eye. At the sametime, streams of air can be projected from the outer tubes 52 and 56with the same relatively high, applied forces so that these streams ofair are adapted to indent the cornea of an eye. The tubes are furtherassociated with pressure responsive means of any conventional type (notshown) for measuring or sensing fluid pressures in the tubes.

In using the tonometer 50, the tubes 52, 54 and 56 can be adjustedrelative to the cornea of an eye for substantially restricting the opentube ends so that the fluid pressure in the center tube is increased toa predetermined level, thereby to locate the tube ends relative to thecornea in the same manner as described above with reference to thedevice 16. The tubes can be further adjusted, if necessary, until fluidpressures in the outer tubes are equal, thereby to assure that the tubesare not tilted relaouter tubes can then be measured as an indication ofintraocular pressure as above described. Although the compressed airsources described with reference to the device 50 have been said toproject streams of air from the outer tubes with relatively high appliedforce and to project a stream of air from the inner tube with relativelylow applied force, a converse arrangement would also be satisfactory.That is, the streams of air projected from the outer passages could beprojected with the relatively low applied force and the stream of airprojected from the center passage could be projected with the relativelyhigh applied force. In such an arrangement, the device could bepositioned relative to the eye for restricting the open tube ends untilthe fluid pressures in the outer tubes were increased to the samepredetermined level, thereby to assure that the tube ends wereproperly-located relative to the eye without being tilted relative to aradius of the cornea. The fluid pressure in the center tube could .thenbe measured as an indication of intraocularpressure.

It should be understood that although particular embodirnents of thetonometer and methods of tonometry provided by this invention have beendescribed for the purpose of illustration, this invention includes allmodifications and equivalents thereof which fall within the open passageend with a selected spacing relative to an .eye; projecting a streamoffluid with selected force from said open passage end through anintervening open space onto-said eye with suflicient force fordistorting said eye against its intraocular pressure; and sensing thedegree of said distortion through said intervening space from a positionspaced from the eye; whereby the degree of said distortion relative tosaid spacing and said force indicate said intraocular pressure. I

3. A method of tonometry comprising as steps: establishing a pluralityof fluid passages having respective open ends in predetermined spatialrelation to each other; projecting streams of fluid from respectivepassages through the open ends thereof, said streams of fluid beingprojected with different forces so that a stream of fluid is projectedfrom at least one passage with suflicient force to indent an eye and astream of fluid is projected from at least one other passage with lessforce than is required for indenting an eye; adjusting the spatialrelationship between the open passage ends and an eye so that the openpassage ends are substantially restricted by the eye and so that the eyeis indented by atleast the stream of fluid projected from said onepassage; measuring fluid pressure within at least said other passage fordeterv mining the spatial relationship between said passage ends andsaid eye; and measuring fluid pressure within at least said one passageas an indication of intraocular pressure.

4. A method of tonometry comprising as steps: establishing a pair offluid passages having respective open ends disposed in side-by-siderelation; projecting a stream and measuring fluid pressure within saidone passage as an indication of intraocular pressure.

I 5. A method of tonometry comprising as steps: providing a pliableprotecting film; disposing the film in coextensive superposition uponthe cornea of an eye; establishing 'a plurality of fluid passages havingrespective open ends disposed in predetermined spatial relation to eachother; projecting stream of fluid from respective passages through theopen ends thereof, said streams of fluid being projected with diflierentforces so that a stream of fluid is projected from at least one passagewith suflicient force to indent an eye; establishing a spatialrelationship between the open passage ends and the cornea of an eyecovered with said film so that said open passage ends are substantiallyrestricted and so that the film and eye are indented by at leastthestream of fluid projected from said one passage; and measuring fluidpressures within said passages asan indication of intraocular pressure.

6. A method of tonometry comprising as steps: establishing a pair offluid Passageshaving respective open ends disposed in predeterminedspatial relation to each other; projecting a stream of fluid from onepassage through tlieopen end, thereof with an applied pressure greaterthan 60 millimeters of mercury; projecting a stream of fluid, ,from theother passage through the-open end thereof. with an applied pressureless than 10 millimeters of mercury; positioning the open, passage endsrelative to an eye for substantially restricting said open passage endsso that fluid pressure within said other passage is increased to apredetermined level slightly less than the pressure applied to fluidwithin said passage and so that the eye is indented by the stream offluid projected from said one passage, thereby to locate the passageends relative to the eye; and measuring fluid pressure within said onepassage as an indication of intraocular pressure.

7. A tonometer comprising means projecting a stream of fluid outwardfrom the tonometer onto an eye with suflicient controlled force from aposition spaced from the eye for distorting the eye against itsintraocular pressure, and means for sensing the degree of saiddistortion from a position spaced from the eye, whereby the degree ofsaid distortion relative to said controlled force can indicate saidintraocular pressure.

8. A tonometer comprising means defining a fluid passage having an openend, means for locating said open passage end in selected spacedrelation to an eye, means for projecting a stream of fluid with selectedforce from said open passage end through an intervening open space ontosaid eye for distorting said eye against its intraocular pressure, andmeans for sensing the degree of said distortion from a position spacedfrom the eye, whereby the degree of said distortion relative to saidspacing of said open passage end and said force indicate said intra-"ocular pressure.

9. A tonometer comprising means having a plurality of passagestherethrough, said passages having respective open ends in closelyspaced relation, means projecting stream of fluid from respectivepassages through the open ends thereof with different applied pressuresso that said "streams offluid are adapted to exert different forces uponan eye and so that at least onestream of fluid is projected withsuflicient force to indent an eye, and means for measuring fluidpressures within each of said passages,

whereby, when said passage means is positioned relative to'an eyeso'that the open passage ends are substantially means for holding saidopen tube ends in predetermined, .closely spacedrelation, such thatsaidopen tube ends can be substantially restricted by an eye, meansprojecting streams of fluid from respective tube means through the openends thereof so that a stream of fluid is projected from at least onetube means with sufficient force for indenting an eye and so that astream of fluid is projected from at least one other tube means withless force than is required for indenting an eye, andpressure-responsive means connected to said tube means for indicatingfluid pressures within respective tube means, whereby said tube meanscan be positioned relative to an eye for substan tially restricting saidopen tube ends so that fluid pressures within said tube means areincreased and so that the eye is indented by at least the stream offluid projected from said one tube means, the fluid pressure within atleast said other tube means can be measured for determining the relativeposition of said tube ends and said eye, and the fluid pressure Withinat least said one tube means can be measured as an indication ofintraocular pressure.

11. A tonometer comprising a pair of tube means having respective openends, means securing said tube means together for maintaining said opentube ends in side-byside relation such that said open tube ends can besubstantially restricted by an eye, means projecting a stream of fluidfrom one tube means through the open end thereof with suflicient forceto indent an eye, means projecting a stream of fluid from the other tubemeans through the open end thereof with less force than is required forindenting an eye, and pressure-responsive means connected to said tubemeans for indicating fluid pressures within said tube means, wherebysaid tube means can be positioned relative to an eye for substantiallyrestricting said open tube ends so that fluid pressure Within said othertube means is increased to a predetermined level and so that the eye isindented by said stream of fluid projected from said one tube means,thereby to locate said open tube ends relative to the eye, and fluidpressure within said one tube means can be measured as an indication ofintraocular pressure.

12. A tonometer comprising a pair of tube means having respective openends, means securing said tube means together for maintaining said opentube ends in concentric relation such that said open tube ends can besubstantially restricted by an eye, means projecting a stream of fluidfrom the inner tube means through the open end thereof with suflicientforce to indent an eye, means projecting a stream of fluid through theopen end thereof with less force than is required for indenting an eye,and pressure-responsive means connected to said tube means forindicating fluid pressures Within said tube means, whereby said tubemeans can be positioned relative to an eye for substantially restrictingsaid open tube ends so that fluid pressure within said outer tube meansis increased to a predetermined level and so that the eye is indented bysaid stream of fluid projected from said inner tube means, thereby tolocate said open tube ends relative to the eye, and fluid pressureWithin said inner tube means can be measured as an indication ofintraocular pressure.

13. A tonometer comprising three tube means having respective open ends,means securing said tube means together for holding said open tube endsin side-by-side linear relation such that said open tube ends can besubstantrally restricted by an eye means projecting a stream of fluidfrom the center tube means through the open end thereof with sufficientforce to indent an eye, means projecting streams of fluid fromrespective outer tube means through the open ends thereof with lessforce than is required for indenting an eye, and pressure-responsivemeans connected to said tube means for indicating fluid pressures withinsaid tube means, whereby said tube means can be positioned relative toan eye for substantially restricting said open tube ends so that fluidpressure Within said outer tube means is increased to a commonpredetermined level and so that the eye is indented by said stream offluid projected from said center tube means, thereby to locate said opentube ends relative to the eye, and fluid pressure within said centertube means can be measured as an indication of intraocular pressure.

14. A tonometer comprising three tube means having respective open ends,means securing said tube means together for holding said open tub endsin side-by-side linear relation, such that said open tube ends can besubstantially restricted by an eye, means projecting streams of fluidfrom respective outer tube means through the open ends thereof withsuflicient force to indent an eye, means projecting a stream of fluidfrom the center tube means through the open end thereof with less forcethan is required for indenting an eye, and pressure-responsive meansconnected to said tube means for indicating fluid pressures within saidtube means, whereby said tube means can be positioned relative to an eyefor substantially restricting said open tube ends so that fluid pressurewith-in said center tube means is increased to a predetermined level, sothat fluid pressures within said outer tube means are increased to acommon level, and so that the eye is indented by the streams of fluidprojected from said outer tube means, thereby to locate said open tubeends relative to the eye, and fluid pressures within said outer tubemeans can b measured as an indication of intraocular pressure.

'15. A tonometer comprising a pair of tube means having respective openends, means securing said tube means together for holding said open tubeends in predeterined, closely spaced relation, means projecting a streamof fluid from one tube means through the open end thereof withsuflicient force to indent an eye, means projecting a stream of fluidfrom the other tube means through the open end thereof with less forcethan is required for indenting an eye, first pressure-responsive meansmeasuring fluid pressure within said one tube means, said firstpressure-responsive means being actuable to record a fluid pressuremeasured by said means, second pressure-responsive means sensing apredetermined fluid pressure within said other passage, and meansassociated with said second pressure-responsive means adapted to actuatesaid first pressure-responsive means when said second pressureresponsivemeans measures a predetermined fluid pressure, whereby the position ofsaid tube means can be adjusted relative to an eye for substantiallyrestricting said open tube ends so that fluid pressure within said othertube means increases to said predetermined level, thereby to locate theopen tube ends relative to the eye, and thereafter fluid pressure withinsaid one tube means will be automatically recorded as an indication ofintraocul-ar pressure.

16. A tonometer comprising a pair of tube means having respective openends, means securing said tube means together for holding said opent-ube ends in predetermined, closely-spaced relation, means projecting astream of fluid from one tube means through the open end thereof withsuflicient force to indent an eye, means projecting a stream of fluidfrom the other tube means through the open end thereof with less forcethan is required for indenting an eye, first manometer means including acolumn of liquid movable in a manometer tube which is connected to saidone tube means so that the liquid level in the manometer tube is adaptedto indicate fluid pressure within said one tube means, valve meansdisposed within said manometer tube which are electrically actuable forfixing the liquid level in said manometer tube, and second manometermeans responsive to fluid pressure within said other tube means, saidsecond manometer means including means adapted to close an electricalcircuit for actuating said valve means when the fluid pressure sensed bysaid second manometer means increases to a predetermined level, whereby,when the position of said tube means is adjusted relative to an eye forsubstantially restricting said open tube ends so that fluid pressureWithin said other tube means is increased to said predetermined leveland so that the stream of fluid projected from said one tube meansindents the eye, said valve means will be automatically actuated forfixing the liquid level in said manometer tube, thereby to record thefluid pressure measured by said first manometer means as an indicationof intraocular pressure.

17. A tonometer comprising a pair of tube means having respective openends, means mounting said tube means for holding said open tube ends inpredetermined, closelyspaced relation, means projecting a stream offluid from one tube means through the open end thereof with sufficientforce to indent an eye, means projecting a stream of fluid from theother tube means through the open end thereof with less force than isrequired for indenting an eye, first manometer means including a columnof liquid movable in a manometer tube which is connected to said onetube means so that the liquid level in the manometer tube is adapted toindicate fluid pressure within said one said manometer tube, valve meansdisposed within said manometer tube which are electrically actuable forfixing tube means, said second manometer means including the liquidlevel in said manometer tube, second manometer means responsive to fluidpressure Within said other twbe means, means detacha-bly mounting ascale adjacent means adapted to close an electrical circuit foractuating said valve means when the fluid pressure sensed by said secondmanometer means increases to a predetermined level, whereby, when theposition of said tube means is adjusted relative to the cornea of an eyefor substantially restricting said open tube ends so that fluid pressurewith in said other tube means is increased to said predetermined leveland so that the stream of fluid projected from said one tube meansinden-ts the cornea, said valve means will be automatically actuated forfixing the liquid level in said manometer tube to record the fluidpressure measured by said first manometer means, and a plurality ofscales adapted to be selectively mounted adjacent said manometer tube,each of said scales having divisions spaced to indicate intraocularpressure corresponding to liquid levels in said manometer tube forrespective corneal curvatures.

18. A method of tonometry comprising as steps: projecting a stream offluid onto an ey with selected force from a position spaced from the eyefor distorting the eye against intraocular pressure, and sensing saiddistortion to measure said intraocular pressure.

19. A tonometer comprising means projecting fluid outward from thetonometer onto an eye with suflicient controlled force from a positionspaced from the eye for distorting the eye against its intraocularpressure, and means for sensing said distortion as a measure of saidintraocular pressure.

20. A method of tonometry comprising the steps of projecting fluid froma position spaced from an eye through an intervening open space onto theeye, said fluid [being projected with a selected .force suflicient fordistorting the eye against its intraocular pressure, and sensing saiddistortion of the eye through an intervening space from a positionspaced from the eye as an indication of said intraocular pressure.

References Cited by the Examiner UNITED STATES PATENTS 5/1955 Zenatti73-80 X 6/1961 Becker 7337.5

1. A METHOD OF TONOMETRY COMPRISING AS STEPS: PROJECTING A STREAM OFFLUID ONTO AN EYE WITH SELECTED FORCE FROM A POSITION SPACED FROM THEEYE FOR DISTORTING THE EYE AGAINST INTRAOCULAR PRESSURE, AND SENSING THEDEGREE OF SAID DISTORTION FROM A POSITION SPACED FROM THE EYE AS ANINDICATION OF SAID INTRAOCULAR PRESSURE.